On Tuesday, September 19, 2017 at 10:59:33 AM UTC+10, George Herold wrote:> On Monday, September 18, 2017 at 6:55:28 PM UTC-4, John Larkin wrote: > > On Mon, 18 Sep 2017 15:35:01 -0700 (PDT), pcdhobbs@gmail.com wrote: > > > > >>Most resistors that are joule rated, including wirewounds, are spec'd > > >>handle X joules for 1 second, and drop off hard for shorter durations. > > >>Some level off at some short time, and some keep tapering off forever > > >>as the times get shorter. > > > > > >Ceramic has a high specific heat but very poor thermal diffusivity compared to metal. At short times all you have to work with is the metal itself. > > > > > >Cheers > > > > > >Phil Hobbs > > > > There are some impressive bulk-ceramic resistors that will absorb > > hundreds of joules in any time domain, but they are gigantic leaded > > parts. Wouldn't fit on a VME board and bad for vibration. > > > > > Carbon composite? or is that too noisy?Carbon has a negative temperature coefficient of resistance and you get hot channels. A former boss had a party piece where he would put roughly an amp through a 0.6W 10k carbon film resistor for half an hour at a time. The resistor still measured 10k afterwards, but it had a dark line in the paint over the top of where the hot channel had been. -- Bill Sloman, Sydney
exploding wirewound resistors
Started by ●September 15, 2017
Reply by ●September 18, 20172017-09-18
Reply by ●September 19, 20172017-09-19
On Mon, 18 Sep 2017 12:43:08 -0500, "Tim Williams" <tmoranwms@gmail.com> wrote:>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >news:g9jurc10cn36es7msu75e50iqgbh92f9fa@4ax.com... >> Did you notice, on my sketch, the parts labeled CURRENT LIMITERS ? >> >>> >>>And the manufacturer, let's not leave them out. Y'think they might know a >>>thing or two about their product? >> >> Why are you being such a smarmy jerk? >> > >Why are you conflating CURRENT LIMITERS with screwdrivers? > > >"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >news:617trchvnvaprp8rhqf0lnucs3dnb5fveh@4ax.com... >> I don't think so. You can fully charge an electrolytic cap and then >> short it with a screwdriver (or a flashtube) and it doesn't seem to >> mind. > >You wrote this, didn't you? > >TimYou aren't worth reading. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 19, 20172017-09-19
On Mon, 18 Sep 2017 16:12:19 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>Den mandag den 18. september 2017 kl. 21.30.52 UTC+2 skrev John Larkin: >> On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin >> <jjlarkin@highland_snip_technology.com> wrote: >> >> > >> > >> >Lots of people make parts like this: >> > >> >https://www.digikey.com/product-detail/en/bourns-inc/PWR5322WR250JE/PWR5322WR250JETR-ND/2022962 >> > >> >The overload specs are almost always 5x rated power for 5 seconds, so >> >a 3 watt part can absorb 15 joules in that time. I wonder what happens >> >for shorter time overloads? Constant joules? >> > >> >Has anyone experimented with stressing this sort of small wirewound >> >resistor? >> > >> >I'll probably order some and blow them up. We'll be using low ohms, >> >0.2 maybe, so we'll need a lot of current. There's a car repair place >> >and a motorcycle shop on our block, so maybe I could buy or borrow a >> >battery. For pure fast joules, I could just discharge some big >> >electrolytics. >> >> Most resistors that are joule rated, including wirewounds, are spec'd >> handle X joules for 1 second, and drop off hard for shorter durations. >> Some level off at some short time, and some keep tapering off forever >> as the times get shorter. >> >> We found a Vishay 3-watt part, WSN6927 at 0.33 ohms, that specs 75 j >> from 1 to 10 seconds, and 10j from 0 to 100 ms, with a slope in the >> gap. That makes our SSR circuit work. I'll get some and blow them up >> to see how much margin we'll have. Maybe pulse them for a few months >> to see if they fatigue. >> >> We'll put eight (!) ADCs on the board to measure channel ON voltage >> drops fast, to shut things down quick if a customer puts a hard >> voltage across one of our SSRs. The series resistor buys us enough >> time to do that. > >how about a IR2127 to do the over current shutdown, seems like it would >be cheaper than that fancy resistor > >http://www.datasheetdir.com/circuits/200/Using-The-Current-Sensing-Ir2125-Ir2127-Ir2128-Gate-Driver-Ics.jpgThe Vishay 3 watt resistor is cheap. We want floating switches, so we'd have to power up that chip somehow. 32 times. And each channel has two fets to protect. If we put a 0.33 ohm, 10 joule or so resistor in series with the fets, the resistor takes most of the voltage drop and dissipation if the customer gives us a hard voltage source up to maybe 75 volts. We'll digitize the voltage drop across each switch (resistor included) and then we know the current and can do the shutdowns in FPGA code. We needed the voltmeter function already for BIST. Really, in the last couple of weeks, we've explored a zillion options, including fuses, self-protecting fets, current limiting the fets, all sorts of crazy schemes... each with at least one fatal flaw. Some loads, like AC relays and solenoids, and bi-level DC relays and solenoids, need high current for a short time to pull in. A fast current limit gives us problems there. We're talking 2 amps continuous, 20 amps for 100 ms, and shutting down ASAP at 100 amps or more. The FPGA can tune all that. Who would have thought that a simple SSR would be so complex? It has been fun, though, brainstorming all those ideas. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●September 19, 20172017-09-19
On Saturday, September 16, 2017 at 11:01:42 AM UTC-7, John Larkin wrote:> Yeah, it looks like the best way to get hundreds of amps in the > millisecond down time frame is to parallel a bunch of electrolytic > caps. Maybe a sheet of copperclad FR4 with a lot of caps soldered or > bolted to the connections on both sides. Where's my Dremel?I'd consider a transformer, myself. I've got a dozen transformers with hundred-amps-capable windings, not sure if any of my capacitors can do that. Faster than millisecond, you need ferrites, but at a millisecond... well, that's about what an auto spark coil is doing. Higher voltage, lower current, but you could rewind one, or just retask a soldering pistol.
Reply by ●September 19, 20172017-09-19
On Fri, 15 Sep 2017 13:16:39 -0700, John Larkin <jjlarkin@highland_snip_technology.com> wrote:> > >Lots of people make parts like this: > >https://www.digikey.com/product-detail/en/bourns-inc/PWR5322WR250JE/PWR5322WR250JETR-ND/2022962 > >The overload specs are almost always 5x rated power for 5 seconds, so >a 3 watt part can absorb 15 joules in that time. I wonder what happens >for shorter time overloads? Constant joules? > >Has anyone experimented with stressing this sort of small wirewound >resistor? > >I'll probably order some and blow them up. We'll be using low ohms, >0.2 maybe, so we'll need a lot of current. There's a car repair place >and a motorcycle shop on our block, so maybe I could buy or borrow a >battery. For pure fast joules, I could just discharge some big >electrolytics.OK, I'm ready to blow up some resistors, as soon as UPS arrives. https://www.dropbox.com/s/u2078h7upn81q10/Z420_3.JPG?raw=1 That should do numbers like 300 amps, 80 joules, 50 volts. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 19, 20172017-09-19
John Larkin wrote...> > We found a Vishay 3-watt part, WSN6927 at 0.33 ohms, > that specs 75 J from 1 to 10 seconds, and 10J from > 0 to 100 ms, with a slope in the gap.Where'd you get that information? Vishay's WSR series is an interesting set of 2W and 3W metal-strip current-sensing parts. -- Thanks, - Win
Reply by ●September 19, 20172017-09-19
On 19 Sep 2017 11:09:49 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >> We found a Vishay 3-watt part, WSN6927 at 0.33 ohms, >> that specs 75 J from 1 to 10 seconds, and 10J from >> 0 to 100 ms, with a slope in the gap. > > Where'd you get that information?Vishay sent us a graph. I guess it's public info.> > Vishay's WSR series is an interesting set of > 2W and 3W metal-strip current-sensing parts.The WSN is non-inductive, Ayrton Perry winding, which we understand has more metal inside than the usual resistors. That helps absorb energy on short time scales. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 19, 20172017-09-19
On a sunny day (Tue, 19 Sep 2017 11:02:38 -0700) it happened John Larkin <jjlarkin@highland_snip_technology.com> wrote in <fom2sctjgp0boousiphreq9j7l7tcrtcgk@4ax.com>:>OK, I'm ready to blow up some resistors, as soon as UPS arrives. > >https://www.dropbox.com/s/u2078h7upn81q10/Z420_3.JPG?raw=1 > >That should do numbers like 300 amps, 80 joules, 50 volts.Why blow anything up? I made this to test 30C lipo batteries, 4 x 1 Ohm 100 W: http://panteltje.com/pub/power_resistors_IMG_6291.JPG http://panteltje.com/pub/big_heatsink_IMG_6292.JPG combine them anyway you want. 99 cent each: http://www.ebay.com/itm/111969905996
Reply by ●September 19, 20172017-09-19
On Mon, 18 Sep 2017 20:37:28 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On Mon, 18 Sep 2017 12:43:08 -0500, "Tim Williams" ><tmoranwms@gmail.com> wrote: > >>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >>news:g9jurc10cn36es7msu75e50iqgbh92f9fa@4ax.com... >>> Did you notice, on my sketch, the parts labeled CURRENT LIMITERS ? >>> >>>> >>>>And the manufacturer, let's not leave them out. Y'think they might know a >>>>thing or two about their product? >>> >>> Why are you being such a smarmy jerk? >>> >> >>Why are you conflating CURRENT LIMITERS with screwdrivers? >> >> >>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >>news:617trchvnvaprp8rhqf0lnucs3dnb5fveh@4ax.com... >>> I don't think so. You can fully charge an electrolytic cap and then >>> short it with a screwdriver (or a flashtube) and it doesn't seem to >>> mind. >> >>You wrote this, didn't you? >> >>Tim > >You aren't worth reading.John's got to be kidding ? You both contrbute worthy information here boB
Reply by ●September 19, 20172017-09-19
On a sunny day (Tue, 19 Sep 2017 12:03:13 -0700) it happened boB <boB@k7iq.com> wrote in <ocq2sc92k5cs7ak654q2kv5bmpeb6t2eth@4ax.com>:>On Mon, 18 Sep 2017 20:37:28 -0700, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>On Mon, 18 Sep 2017 12:43:08 -0500, "Tim Williams" >><tmoranwms@gmail.com> wrote: >> >>>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >>>news:g9jurc10cn36es7msu75e50iqgbh92f9fa@4ax.com... >>>> Did you notice, on my sketch, the parts labeled CURRENT LIMITERS ? >>>> >>>>> >>>>>And the manufacturer, let's not leave them out. Y'think they might know a >>>>>thing or two about their product? >>>> >>>> Why are you being such a smarmy jerk? >>>> >>> >>>Why are you conflating CURRENT LIMITERS with screwdrivers? >>> >>> >>>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >>>news:617trchvnvaprp8rhqf0lnucs3dnb5fveh@4ax.com... >>>> I don't think so. You can fully charge an electrolytic cap and then >>>> short it with a screwdriver (or a flashtube) and it doesn't seem to >>>> mind. >>> >>>You wrote this, didn't you? >>> >>>Tim >> >>You aren't worth reading. > >John's got to be kidding ? > >You both contrbute worthy information here > >boBActually in the flash tube designs I did I used a small inductor in series to limit the current. Else BAD THINGS can happen.
